Sodium sulphate flotation



Patented Feb. 9, 1943 SODIUM SULPHATE FLOTATION David J. lPye, Walnut Creek, Califl, assignor to The Dow Chemical Company, Midland, Mich, a

corporation of Michigan No Drawing. Application ()ctobcr 7, 1940, Serial No. 360,116

Claims.

This invention relates to the separation of crystalline sodium sulphate from crystalline sodium chloride by flotation. Intimate, substantially homogeneous mixtures of these crystalline materials in varying proportions can occur as a result of various operations. Attempts to remove the sodium sulphate from the sodium chloride crystals by fractional crystallization, for example, are relatively diificult and expensive.

I have found that sodium sulphate can be successfully separated from sodium chloride by a simple and inexpensive froth flotation operation.

In carrying on a separation according to the present invention the bowl of a Fagergren laboratcry flotation cell was filled with 2500 cc. of a mother liquor carrying about 600 grams of a crystalline mixture of the two salts. The crystals were first placed in the cell and the cell was then filled with a brine made up by dissolving some of the mixture in distilled water to saturation.

The flotation machine rotor was started with the air passage closed and was permitted to run for three minutes. A suitable non-metallic mineral flotation agent and a suitable frother as pine oil were then added and the cell contents conditioned with continued agitation. Thereafter the air cock was opened slightly and the froth taken off. This procedure resulted in a reduction of the sulphate content from 4.6% to 0.37%, a reduction of 92% in the sulphate content of the crystalline sodium chloride. The accompanying loss of sodium chloride was only 0.9%.

The sodium chloride-sodium sulphate ratio is not critical and the separation is eflective even though the ratio of the two crystal materials varies over a wide range.

The mother liquor can contain materials other than sodium sulphate and sodium chloride; for example, in one operation it contained about 1% sodium hydroxide, about 0.5% sodium carbonate and about 0.045 pound of lime per ton. The presence of these other materials in the mother liquor does not interfere with the flotation operation. A temperature of about 23 C.- room temperature-was maintained during the flotation operation although this is not critical.

In some operations it was found advantageous to add the flotation agent in successive steps,

three times.

While oleic acid has been employed preferably as the flotation agent, it is, of course, to be understood that the flotation operation can be conducted with any other suitable flotation agent such as stearic acid, palmitic acid or other fatty acids and with source materials for such fatty acids as fish oils and the like.

The presence of a small amount of an ion of an element having a substantially water insoluble sulphate and a soluble chloride appears to have a very beneficial effect in conditioning the salt mixture for flotation, particularly in reducing the amount of sodium chloride removed with the sodium sulphate. For example, by adding lime equivalent to l0%-15% of the oleic acid and decreasing the oleic acid employed from 1 pound per ton to 0.1 pound per ton, the sodium chloride loss was decreased from 21.2% to 4%, although the sodium sulphate removal was decreased from to 83%. It appears that when an ion of one of the presently named elements is employed with a fatty acid, the fatty acid should not be present in excess of that required stoichiometrically to form the fatty acid soap of the element. Such elements are calcium, barium, strontium, titanium and ferric iron; the element employed can be present in the brine as a constituent thereof or else added to the brine or to the mixture in the form of a suitable compound. The element should be available apparently in ionic form to condition the mixture for flotation.

I claim:

1. A process for separating sodium chloride crystals from sodium sulphate crystals which comprises subjecting a pulp of said crystals in an alkaline brine containing sodium hydroxide to a froth flotation process employing an agent selected from the group consisting of a fatty acid, a fatty acid soap and a fatty acid ester and a material supplying an ion selected from the groups consisting of calcium, barium, strontium, titanium and iron in the ferric state to float off selectively the sodium sulphate crystals from the sodium chloride crystals.

2. A process for separating sodium chloride crystals from sodium sulphate crystals which comprises subjecting a pulp of said crystals in a saturated brine to a froth flotation operation in the presence of a material selected from the group consisting of a fatty acid, a fatty acid soap and a fatty acid ester and a material supplying an ion selected from the group consisting of calcium, barium, strontium, titanium and iron in the ferric state.

3. A process for separating a mixture of sodium sulphate crystals from sodium chloride crystals comprising subjecting a pulp of said mixture in its saturated brine to a froth flotation operation in the presence of oleic acid and a material supplying an ion selected from the group consisting of calcium, barium, strontium, titanium and iron in the ferric state.

4. A process for separating a mixture of sodium sulphate crystals from sodium chloride crystals comprising subjecting a pulp of said mixture in its saturated brine to a froth flotation operation in the presence of about 0.1 pound of oleic acid per ton of mixture and a material selected from 

